@IBAction func Stopwatch (Sender:UIButton) { 
 
var startTime = NSTimeInterval()
 
    func updateTime(timer:NSTimer) {
 
        //Find Current TIme
 
        var currentTime = NSDate.timeIntervalSinceReferenceDate()
 
        //Find the difference between current time and start time
 
        var elapsedTime :NSTimeInterval = currentTime - startTime
 
        //calculate the minutes in elapsed time.
        let minutes = UInt(elapsedTime / 60.0)
        elapsedTime -= (NSTimeInterval(minutes) * 60)
 
        //calculate the seconds in elapsed time.
        let seconds = UInt(elapsedTime)
        elapsedTime -= NSTimeInterval(seconds)
 
        //find out the fraction of milliseconds to be displayed.
        let hours = UInt(elapsedTime * 100)
 
        let strMinutes = minutes > 9 ? String(minutes):String(minutes)
        let strSeconds = seconds > 9 ? String(seconds):String(seconds)
        let strHours = hours > 9 ? String(hours):String(hours)
 
        //assign text to Label
        elapsedTimeLabel.text = "You have slept for \(strHours)"
    }
 
    //Timer 
    var timer = NSTimer.scheduledTimerWithTimeInterval(0.5,target: self,selector: Selector("updateTime:"),userInfo: nil,repeats: true)
    startTime = NSDate.timeIntervalSinceReferenceDate()
 
}
}

每次我运行应用程序(在iOS模拟器中)时,按下按钮时应用程序崩溃(执行秒表功能).错误总是会读取

2014-11-23 11:44:53.617 Sleep[9630:644637] -[Sleep.FirstViewController updateTime:]: 
unrecognized selector sent to instance 0x7ff6d9676e80
2014-11-23 11:44:53.622 Sleep[9630:644637] *** Terminating app due to uncaught exception 
'NSInvalidArgumentException',reason: '-[Sleep.FirstViewController updateTime:]: unrecognized 
selector sent to instance 0x7ff6d9676e80'
*** First throw call stack:

我不知道为什么会这样,我对iOS编程很新,所以请帮忙！